Did you make this instructable?

This one, unlike the others, is something he might actually accomplish. (Proof: There was a news story on NPR this morning about a 15yo who, with his father's help, designed and implemented a homebrew electric conversion on a VW Super Beetle. But he can't dive it on public roads yet -- he needs to be 16 to get his learner's permit.)

Still, if he's gonna try, this is a better direction for him to be trying in. He may have to scale his project back to an electric go-cart or electric bicycle, but he should be able to get _something_ running if he's serious about it... and in the process would learn something about how to take an idea from "wouldn't it be nice if" to something that actually works. And if he isn't yet ready to make a serious attempt, he'll learn that too.

A man carrying vehicle needs to have a certain amount of POWER available. For example an average human can output about half a horse power over any reasonable length of time.

1 HP=746 watts

So to = a humans effort you need around 360 watts available.

From a practical point of view I know that 250 watts can drive a single 115 pound driver at about 30 MPH. This can be sustained for around 2 hours over fairly flat ground from 2 x 75 Amp hr car batteries.

Remember: No matter what you do, wattage remains constant. You can easily get 20 times the voltage, but only at 1/20th of the amperage, minus a bit for inefficiencies in conversion. If what you've got is 12V batteries, you're better off using 12V components.... or stacking up batteries in series, if you want more voltage

This is a large part of why building an electric car is hard. To provide a lot of power, you need a lot of batteries, which take a lot of space and weigh a lot.